Lubricating oil compositions

ABSTRACT

A trunk piston marine diesel engine lubricating oil composition is dispersant-free, has a TBN of 25 or greater, and comprises  
     (A) an oil of lubricating viscosity,  
     (B) an aromatic carboxylate as the sole overbased metal detergent, and  
     (C) an antiwear additive.

[0001] This invention relates to a trunk piston marine enginelubricating composition for a medium speed 4-stroke compression-ignited(diesel) marine engine and lubrication of such a trunk piston engine.

[0002] The term “marine” does not restrict the engines to those used inwater-borne vessels; as is understood in the art, it also includes thosefor auxiliary power generation applications and for main propulsionstationary land-based engines of the above types for power-generation.

[0003] One problem associated with trunk piston engines is that theirmanufacturers commonly design them to use a variety of diesel fuels,ranging from good quality high distillate fuel with low sulfur and lowasphaltene content to poorer quality intermediate or heavy fuel such as“Bunker W or residual fuel oil with generally higher sulfur and higherasphaltene content. Lubricants used in such engines often becomecontaminated with asphaltene components from the fuel, leading tocleanliness problems in service, sometimes referred to as “black paint”.

[0004] Lubricating oils compositions (or lubricants) for trunk pistonengines are known and may be referred to as trunk piston engine oils orTPEO's. They are known to include, as additives to improve theirperformance, ashless dispersants and overbased detergents.

[0005] EP-A-0-662 508 meets the above problem by describing use of acomposition that includes a hydrocarbyl-substituted phenate concentratehaving a TBN greater than 300, and at least one of ahydrocarbyl-substituted salicylate and a hydrocarbyl-substitutedsulphonate. However, the composition also includes, apparently, adispersant since the EP states that lubricating oils for medium speeddiesel engines typically comprise dispersants to minimise depositformation in various parts of the engine.

[0006] Thus, EP-A-0-662 508 requires several additives to meet theproblem, thus increasing cost in a cost-sensitive environment.

[0007] It has now surprisingly been found that a dispersant-free TPEO,wherein the overbased metal detergent is of the aromatic carboxylate,such as salicylate, type only, provides excellent performance in severalrespects, i.e. without the need for certain additional additives asrequired by the prior art, for example any other overbased metaldetergents, such as overbased phenates or overbased sulfonates.

[0008] Accordingly, a first aspect of the present invention is a trunkpiston marine engine lubricating oil composition for a medium speedcompression-ignited (diesel) marine engine wherein the composition isdispersant-free and has a Total Base Number (TBN) of 25 or greater, andcomprises:

[0009] (A) an oil of lubricating viscosity, in a major amount, and addedthereto:

[0010] (B) an oil-soluble overbased metal detergent additive, as thesole overbased metal detergent, consisting of one or more aromaticcarboxylates, in a minor amount, and

[0011] (C) an antiwear additive, in a minor amount.

[0012] A second aspect of the present invention is trunk piston marineengine lubricating oil composition for a medium speedcompression-ignited (diesel) marine engine wherein the composition isdispersant-free and has a Total Base Number (TBN) of 25 or greater, andcomprises:

[0013] (A) an oil of lubricating viscosity, in a major amount, and addedthereto:

[0014] (B) an oil-soluble overbased metal detergent additive consistingof, as the sole metal detergent, one or more hydrocarbyl-substitutedsalicylates, in a minor amount, and

[0015] (C) an antiwear additive comprising a dihydrocarbyldithiophosphate metal salt, in a minor amount.

[0016] A third aspect of the present invention is the use of additives(B) and (C) as defined in the first or second aspect of the invention ina dispersant-free trunk piston marine engine oil lubricating compositionhaving a TBN of 25 or greater to (a) suspend asphaltene components inthe composition, or (b) control piston deposits, or both (a) and (b),when used in a medium speed compression-ignited marine engine.

[0017] A fourth aspect of the present invention is a method oflubricating a medium speed compression-ignited marine engine whichcomprises supplying to the engine the trunk piston marine engine oillubricating composition according to the first or second aspect of theinvention.

[0018] “Major amount” means in excess of 50 mass % of the composition.

[0019] “Minor amount” means less than 50 mass % of the composition, bothin respect of the stated additive and in respect of the total mass % ofall the additives present in composition, reckoned as active ingredientof the additive or additives.

[0020] “Comprises or comprising” or cognate words is taken to specifythe presence of stated features, steps, integers or components, but doesnot preclude the presence or addition of one or more other features,steps, integer components or groups thereof.

[0021] “TBN” (Total Base Number) is as measured by ASTM D2896, and theviscosity index is as defined by ASTM D2270.

[0022] The features of the invention will now be discussed in moredetail below.

[0023] Marine Diesel Engines

[0024] The lubricating oil composition of the present invention may besuitable for use in a 4-stroke trunk piston engine having an enginespeed of 200 to 2,000 e.g. 400 to 1,000, rpm, and a brake horse-power(BHP) per cylinder of 50 to 3,000, preferably 100 to 2,000.

[0025] Lubricating Oil Composition

[0026] Preferably, the TBN of the lubricant composition is in the rangeof from 25 to 100, such as from 25 or 30 to 60, preferably 40 to 55.

[0027] Preferably, the viscosity index of the lubricant composition isat least 90, more preferably at least 95, and at most 140 such as 120,preferably 110. A preferred viscosity index range is from 95 to 115.

[0028] The lubricant composition may, for example, have a kinematicviscosity at 100° C. (as measured by ASTM D445) of at least 9,preferably at least 13, more preferably in the range of from 14 to 24,for example from 14 to 22, mm²s⁻¹.

[0029] (A) Oil of Lubricating Viscosity

[0030] The oil of lubricating viscosity (sometimes referred to aslubricating oil) may be any oil suitable for the lubrication of a trunkpiston engine. The lubricating oil may suitably be an animal, avegetable or a mineral oil. Suitably the lubricating oil is apetroleum-derived lubricating oil, such as a naphthenic base, paraffinicbase or mixed base oil. Alternatively, the lubricating oil may be asynthetic lubricating oil. Suitable synthetic lubricating oils includesynthetic ester lubricating oils, which oils include diesters such asdi-octyl adipate, di-octyl sebacate and tridecyl adipate, or polymerichydrocarbon lubricating oils, for example liquid polyisobutene andpoly-alpha olefins.

[0031] Commonly, a mineral oil is employed. The lubricating oil maygenerally comprise greater than 60, typically greater than 70, mass % ofthe composition, and typically have a kinematic viscosity at 100° C. offrom 2 to 40, for example from 3 to 15, mm²s⁻¹ and a viscosity index offrom 80 to 100, for example from 90 to 95.

[0032] Another class of lubricating oils is hydrocracked oils, where therefining process further breaks down the middle and heavy distillatefractions in the presence of hydrogen at high temperatures and moderatepressures. Hydrocracked oils typically have a kinematic viscosity at100° C. of from 2 to 40, for example from 3 to 15, mm²s⁻¹ and aviscosity index typically in the range of from 100 to 110, for examplefrom 105 to 108. The lubricating compositions of the present inventionare free of dispersants in the sense of containing substantially nodispersant. The lubricating composition in every aspect of the presentinvention may, however, contain small amounts of a dispersant, providedthe composition does not substantially demonstrate the dispersancyeffect of the component.

[0033] A dispersant is an additive for a lubricating composition whoseprimary function is to hold solid and liquid contaminants in suspension,thereby passivating them and reducing engine deposits at the same timeas reducing sludge depositions. Thus, for example, a dispersantmaintains in suspension oil insoluble substances that result fromoxidation during use of the lubricating oil, thus preventing sludgeflocculation and precipitation or deposition on metal parts of theengine.

[0034] A noteworthy class of dispersants are “ashless”, meaning anon-metallic organic material that forms substantially no ash oncombustion, in contrast to metal containing, hence ash-forming,materials. Ashless dispersants comprise a long chain hydrocarbon with apolar head, the polarity being derived from inclusion of, e.g. an O, Por N atom. The hydrocarbon is an oleophilic group that confers oilsolubility, having for example 40 to 500 carbon atoms.

[0035] Thus, ashless dispersants may comprise an oil-soluble polymerichydrocarbon backbone having functional groups that are capable ofassociating with particles to be dispersed.

[0036] (B) Overbased Metal Detergent

[0037] A detergent is an additive that reduces formation of pistondeposits, for example high-temperature varnish and lacquer deposits, inengines; it has acid-neutralising properties and is capable of keepingfinely divided solids in suspension. It is based on metal “soaps”, thatis metal salts of acidic organic compounds, sometimes referred to assurfactants, which, in the present case, is an aromatic carboxylic acidonly, such as salicylic acid.

[0038] The aromatic moiety of the aromatic carboxylic acid can containheteroatoms, such as nitrogen. Preferably, the moiety contains onlycarbons atoms. The moiety may contain at least 4 carbon atoms,preferably six or more carbon atoms; for example benzene is a preferredmoiety.

[0039] The aromatic carboxylic acid surfactant may contain one or morearomatic moieties, such as one or more benzene rings, either fused orconnected via alkylene bridges.

[0040] Preferably the carboxylic acid group is attached directly to acarbon atom on the aromatic moiety, such as on the benzene ring.

[0041] More preferably, the aromatic moiety also contains a secondfunctional group, such as a hydroxy group or a sulfonate group, whichcan be attached directly or indirectly to a carbon atom on the aromaticmoiety.

[0042] The detergent comprises a polar head with a long hydrophobictail; the polar head comprises a metal salt of the aromatic carboxylicacid, such as salicylic acid. Large amounts of a metal base are includedby reacting an excess of a metal compound, such as an oxide orhydroxide, with an acidic gas such as carbon dioxide to give anoverbased detergent which comprises a neutralised detergent, such as ametal salt of a surfactant and a metal base (e.g. carbonate) micelle.

[0043] The overbased detergents of this invention may have a TBN in therange of 60 to 600, preferably 100 to 450, more preferably 160 to 400.

[0044] The metal may be an alkali or alkaline earth metal, e.g., sodium,potassium, lithium, calcium, and magnesium. Calcium is preferred.

[0045] Surfactants for the surfactant system of the overbased metaldetergents can contain at least one hydrocarbyl group, for example, as asubstituent on an aromatic ring. Preferably the aromatic carboxylicacids effective in the present invention have a hydrocarbyl groupattached directly to a carbon atom on the aromatic moiety.

[0046] The term “hydrocarbyl” as used herein means that the groupconcerned is primarily composed of hydrogen and carbon atoms and isbonded to the remainder of the molecule via a carbon atom, but does notexclude the presence of other atoms or groups in a proportioninsufficient to detract from the substantially hydrocarboncharacteristics of the group. Advantageously, hydrocarbyl groups insurfactants for use in accordance with the invention are aliphaticgroups, preferably alkyl or alkylene groups, especially alkyl groups,which may be linear or branched. The total number of carbon atoms in thesurfactants should be at least sufficient to impact the desiredoil-solubility.

[0047] The hydrocarbyl group may contain contain 5 to 100, preferably 9to 30, especially 14 to 20, carbon atoms.

[0048] Aromatic carboxylates, preferably salicylates, used in accordancewith the invention may be non-sulfurized or sulfurized, and may bechemically modified and/or contain additional substitutents. Process forsulfurizing, for example a hydrocarbyl-substituted salicylic acid, arewell known to those skilled in the art.

[0049] Salicylic acids are typically prepared by the carboxylation, bythe Kolbe-Schmitt process, of phenoxides, and in that case, willgenerally be obtained, normally in a diluent, in admixture withuncarboxylated phenol.

[0050] Preferred substituents in oil-soluble salicylic acids from whichsalicylates in accordance with the invention may be derived are alkylsubstituents. In alkyl—substituted salicylic acids, the alkyl groupsadvantageously contain 5 to 100, preferably 9 to 30, especially 14 to20, carbon atoms. Where there are more than one alkyl groups, theaverage number of carbon atoms in all of the alkyl groups is preferablyat least 9 to ensure adequate oil-solubility.

[0051] The aromatic carboxylates, such as salicylates, may be used in aproportion in the range of 0.5 to 30, preferably 2.5 to 15 or to 20,mass % based on the mass of the lubricating oil composition.

[0052] A preferred overbased metal detergent is a calcium salicylate.

[0053] (C) Antiwear Additive

[0054] This reduces friction and excessive wear and is usually based oncompounds containing sulfur or phosphorus or both, for example that arecapable of depositing polysulfide films on the surfaces involved.Noteworthy are dihydrocarbyl dithiophosphate metal salts, whichconstitute preferred anti-wear additives in the present invention.

[0055] The metal in the dihydrocarbyl dithiophosphate metal may be analkali or alkaline earth metal, or aluminium, lead, tin, molybdenum,manganese, nickel or copper.

[0056] Zinc salts are preferred as the antiwear additive.

[0057] Preferably the antiwear additive, such as the metal dihydrocarbyldithiophosphate salt, is present in the range of 0.1 to 1.5, preferably0.5 to 1.3, mass %, based upon the total mass of the lubricating oilcomposition.

[0058] The metal dihydrocarbyl dithiophosphate salts may be prepared inaccordance with known techniques by first forming a dihydrocarbyldithiophosphoric acid (DDPA), usually by reaction of one or more alcoholor a phenol with P₂S₅ and then neutralizing the formed DDPA with a zinccompound. For example, a dithiophosphoric acid may be made by reactingmixtures of primary and secondary alcohols. Alternatively, multipledithiophosphoric acids can be prepared comprising both hydrocarbylgroups that are entirely secondary in character and hydrocarbyl groupsthat are entirely primary in character. To make the zinc salt, any basicor neutral zinc compound may be used but the oxides, hydroxides andcarbonates are most generally employed. Commercial additives frequentlycontain an excess of zinc due to use of an excess of the basic zinccompound in the neutralisation reaction.

[0059] The preferred zinc dihydrocarbyl dithiophosphates are oil-solublesalts of dihydrocarbyl dithiophosphoric acids and may be represented bythe following formula:

[(RO)(R¹O)P(S)]₂Zn

[0060] where R and R¹ may be the same or different hydrocarbyl radicalscontaining from 1 to 18, preferably 2 to 12, carbon atoms and includingradicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl andcycloaliphatic radicals. Particularly preferred as R and R′ groups arealkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, forexample, be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl,amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl,2-ethylehexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl,propenyl, butenyl. In order to obtain oil-solubility, the total numberof carbon atoms (i.e. in R and R¹) in the dithiophosphoric acid willgenerally be 5 or greater. The zinc dihydrocarbyl dithiophosphate cantherefore comprise zinc dialkyl dithiophosphates.

[0061] Examples of ashless, i.e. non metal-containing, anti-wear agentsinclude 1,2,3-trizoles, benzotriazoles, thiadiazoles, sulfurised fattyacid esters, and dithiocarbamate derivatives.

[0062] Other additives such as pour point depressants, anti-foamants,and/or demulsifiers may be provided, if necessary.

[0063] It may be desirable, although not essential, to prepare one ormore additive packages or concentrates comprising the additives, wherebyadditives (B) and (C) can be added simultaneously to the base oil toform the lubricating oil composition. Dissolution of the additivepackage(s) into the lubricating oil may be facilitated by solvents andby mixing accompanied with mild heating, but this is not essential. Theadditive package(s) will typically be formulated to contain theadditive(s) in proper amounts to provide the desired concentration,and/or to carry out the intended function in the final formulation whenthe additive package(s) is/are combined with a predetermined amount ofbase lubricant. Thus, additives (B) and (C), in accordance with thepresent invention, may be admixed with small amounts of base oil orother compatible solvents together with other desirable additives toform additive packages containing active ingredients in an amount, basedon the additive package, of, for example, from 2.5 to 90, preferablyfrom 5 to 75, most preferably from 8 to 60, mass % of additives in theappropriate proportions, the remainder being base oil.

[0064] The final formulations may typically contain about 5 to 40 mass %of the additive packages(s), the remainder being base oil.

[0065] The term ‘active ingredient’ (a.i.) as used herein refers to theadditive material that is not diluent.

[0066] The terms ‘oil-soluble’ or ‘oil-dispersable’ as used herein donot necessarily indicate that the compounds or additives are soluble,dissolvable, miscible or capable of being suspended in the oil in allproportions. These do mean, however, that they are, for instance,soluble or stably dispersible in oil to an extent sufficient to exerttheir intended effect in the environment in which the oil is employed.Moreover, the additional incorporation of other additives may alsopermit incorporation of higher levels of a particular additive, ifdesired.

[0067] The lubricant compositions of this invention comprise definedindividual (i.e. separate) components that may or may not remain thesame chemically before and after mixing.

EXAMPLES

[0068] The present inventions is illustrated by, but in no way limitedto, the following examples.

[0069] Components

[0070] The components used in the examples were as follows.

[0071] Overbased Metal Detergents:

[0072] B1—an overbased calcium salicylate having a TIBN of 168, afterdilution.

[0073] B2—an overbased calcium salicylate having a TBN of 280, afterdilution.

[0074] Anti-wear Additives

[0075] C1—a zinc dialkyldithiophosphate (ZDDP) made from a primary C8alcohol.

[0076] Other Components

[0077] T—antifoamant

[0078] Lubricant Compositions and Tests

[0079] Lubricant compositions as trunk piston marine diesel lubricatingoils were prepared by admixing with a basestock the components B1 and B2and component C1, and optionally component T, as identified above. Theadmixing was carried out by blending at elevated temperature. Twocompositions were prepared to have the following formulations: ComponentOil 1 Oil 2 B1 10.10 12.50 B2 5.65 6.84 C1 0.61 0.61 T 10 ppm — Base OilBalance Balance TBN 30 40

[0080] Unless otherwise stated, the figures above represent mass %values, based on the mass of the composition.

[0081] Oil 1 and Oil 2, being compositions of the invention, were testedas described below, as were the following comparison compositions, beingat some stage commercially available.

[0082] Reference Oil 1: has a TBN of 30; comprises, as overbaseddetergent, a combination of calcium phenate and calcium sulfonate; asantiwear additive, a zinc dialkyldithiophosphate; and apolyalkenyl-substituted succinimide dispersant.

[0083] Reference Oil 2: as Reference Oil 1 but having, as overbaseddetergent, a combination of calcium phenate, calcium salicylate andcalcium sulfonate.

[0084] Reference Oil 3: as Reference Oil 1 having a TBN of 40.

[0085] Each of the above-described compositions was tested by using themto lubricate a Wartsila 4L20 trunk piston power generation 4-stroke,heavy fuelled, diesel engine for 500 hours. At the beginning of eachtest, engine components were clean and within the manufacturer'sspecification. At the end of each test, the pistons (4) were removed andexamined as follows:

[0086] Rating (i) visually for ring grooves fillings to provide apercentage of the uppermost groove (Groove 1) and the next lower groove

[0087] (Groove 2) that is filled with deposit;

[0088] Rating (ii) visually for overall piston rating expressed as aweighted demerit according to the Caterpillar 1-K method; and

[0089] Rating (iii) measuring the amount of deposit, expressed as itsdepth in microns as an area-weighted average, on the walls of theoil-cooling gallery (sometimes referred to as “undercrown , or UC,deposits”).

[0090] Rating (i) and rating (ii) were performed according to the CRCrating procedure described in the CRC Manual No. 18 (1991), and rating(iii) was performed as described in the Wartsila-NSD procedure ‘TheLimits for Deposit Thicknesses and Component Wear in Connection withLubricating Oil Approval Tests, MSLWD2.DOC (Feb. 1, 1999)’. The resultsof rating (iii) provide an indication of the ability of the compositionto combat the “black paint” problem referred to hereinbefore.

[0091] Results

[0092] The results of the above tests, reported as an average over the 4cylinders, are summarised below: Rating (i) Ring Groove Ring GrooveRating (ii) Rating (iii) COMPOSITIONS 1 2 Demerit UC Deposits Oil 1 6.250.00 381 25.90 Reference Oil 1 37.25 15.75 1,433 74.10 Reference Oil 14.25 5.00 1,066 67.40 Oil 2 0.00 0.50 527 21.60 Reference Oil 3 8.002.50 1,198 46.80

[0093] For each rating, lower values represent a superior performance.The results show that, for the compositions of TBN 30, the compositionof the invention (Oil 1) is better in almost all tests than thecomparison compositions (Reference Oils 1 and 2). They also show that,for compositions of TBN 40, the composition of the invention (Oil 2) isbetter in all tests than the comparison composition (Reference Oil 3).

1. A trunk piston marine engine lubricating oil composition for a mediumspeed compression-ignited (diesel) marine engine wherein the compositionis dispersant-free and has a Total Base Number (TBN) of 25 or greater,and comprises: (A) an oil of lubricating viscosity, in a major amount,and added thereto: (B) an oil-soluble overbased metal detergentadditive, as the sole overbased metal detergent, consisting of one ormore aromatic carboxylates, in a minor amount, and (C) an antiwearadditive, in a minor amount.
 2. A trunk piston marine engine lubricatingoil composition for a medium speed compression-ignited (diesel) marineengine wherein the composition is dispersant-free and has a Total BaseNumber (TBN) of 25 or greater, and comprises: (A) an oil of lubricatingviscosity, in a major amount, and added thereto: (B) an oil-solubleoverbased metal detergent additive consisting of, as the sole metaldetergent, one or more hydrocarbyl-substituted salicylates, in a minoramount, and (C) an antiwear additive comprising a dihydrocarbyldithiophosphate metal salt, in a minor amount.
 3. The composition asclaimed in claim 1 or claim 2 further comprising a fuel oil with aresidual fuel content, in a minor amount.
 4. The composition as claimedin any one of the preceding claims having a TBN in the range of 25 to100, such as 25 or 30 to
 60. 5. The composition as claimed in any one ofthe preceding claims wherein component (B) is present in the compositionin an amount in the range of 0.5 to 30 mass %.
 6. The composition asclaimed in any one of the preceding claims wherein the one or moreoverbased metal detergent has or have a TBN in the range of 60 to 600,such as 100 to 450, preferably 160 to
 400. 7. The composition as claimedin any one of the preceding claims wherein the one or more overbasedmetal detergent is or are calcium salicylates.
 8. The composition asclaimed in any one of the preceding claims, wherein the antiwearadditive is a zinc salt.
 9. The use of additives (B) and (C) as definedin any one of the preceding claims in a dispersant-free trunk pistonmarine engine oil lubricating composition having a TBN of 25 or greaterto (a) suspend asphaltene components in the composition, or (b) controlpiston deposits, or both (a) and (b), when used in a medium speedcompression-ignited marine engine.
 10. A method of lubricating a mediumspeed compression-ignited marine engine which comprises supplying to theengine the truck piston marine engine oil lubricating composition asclaimed in any one of claims 1 to 8.